1. Field of the Invention
The present invention relates to a liquid electrophotographic printer, and more particularly, to a liquid electrophotographic printer having an improved drying device for drying a photoreceptor belt.
2. Description of the Related Art
An electrophotographic printer such as a laser printer generally employs a mechanism for supplying a developer having a predetermined color to a photosensitive medium, such as a photoreceptor drum or a photoreceptor belt, on which a latent electrostatic image is formed, and developing the latent electrostatic image into a toner image.
The developer is divided into either a liquid type developer or a powder type developer. The liquid type developer has a fine particle toner having a predetermined color dispersed in a volatile liquid carrier. The liquid laser printer using a liquid type developer has a better printing quality than the dry laser printer using only a powder toner, and can be protected from harmful toner powder. Therefore, the liquid type developer is being increasingly used.
Referring to FIG. 1, a conventional image developing apparatus includes a photoreceptor belt 110 on an endless track, and first, second and third rollers 121, 122 and 123 for circulating the photoreceptor belt 110 along the endless track. The third roller 123 is a driving roller driven by a driving motor (not shown) for rotating the photoreceptor belt 110, and the second roller 122 is a steering roller for preventing meandering by adjusting the tension of the photoreceptor belt 110. In FIG. 1, reference numeral 124 represents a transfer roller for transferring the toner image formed on the photoreceptor belt 110 to a sheet of paper 126, and reference numeral 125 is a pressing roller for pressing the sheet 126 against the transfer roller 124. Also, reference numeral 150 is a drying device for removing a liquid carrier from the toner image formed by a development device to be described later.
A charging station 135 for charging the photoreceptor belt 110 is positioned in the vicinity of the carrying area of the photoreceptor belt 110 between the first and second rollers 121 and 122. In the carrying area of the photoreceptor belt 110 between the second and third rollers 122 and 123, there are alternately installed a plurality of laser scanning units (LSUs) 130 for forming a latent electrostatic image on the photosensitive region of the photoreceptor belt 110 by irradiating laser beams onto the photoreceptor belt 110, and a plurality of development devices 140 for developing the latent electrostatic image into the toner image by applying a developer liquid having a toner of a predetermined color to a region where the latent electrostatic image is formed.
The toner image of the photoreceptor belt 110 is transferred to the sheet 126 by the transfer roller 124 after being dried by the drying device 150.
Referring to FIG. 2, a development roller 141, a cleaning roller 142, and squeegee rollers 144 and 146 are disposed on the upstream side of the development device 140. The development roller 141 applies a developer liquid 148 supplied from a developer liquid supplier 143 to the latent electrostatic image formed on the photoreceptor belt 110. The cleaning roller 142 removes the excess developer liquid from the developer liquid supplier 143 which remains on the surface of the development roller 141. The squeegee rollers 144 and 146 remove excess developer liquid 148 remaining after being used in developing the latent electrostatic image. The developer liquid 148 sticking to the squeegee rollers 144 and 146 is separated by blades 145 and 147 being in contact with the surfaces of the squeegee rollers 144 and 146 to then be recovered and stored in the development device 140.
The toner image of the photoreceptor belt 110, having passed through the squeegee rollers 144 and 146, is formed into a thin-film like liquid toner image. The liquid carrier remaining in the toner image is removed while passing through a drying device 150. The drying device 150 includes a dry roller 151, a heat roller 153 and a collector 155.
The dry roller 151 absorbs the liquid carrier of the toner image while rotating in contact with the photoreceptor belt 110. An absorption layer 152 for absorbing the liquid carrier is formed on the dry roller 151. The heat roller 153 contacts the dry roller 151 and is provided with a heat source such as a halogen lamp 154. The heat roller 153 heats the surface of the dry roller 151 using the heat generated from the halogen lamp 154 to evaporate the liquid carrier absorbed into the absorption layer 152 of the dry roller 151. The collector 155 collects and recovers the gaseous carrier generated in the dry roller 151.
As described above, the conventional liquid laser printer has the following disadvantages.
First, since a dry roller heated at a high temperature directly contacts a photoreceptor belt, the life of the photoreceptor belt is shortened due to thermal stress.
Second, when the excess developer liquid is not sufficiently removed from the photoreceptor belt, the carrier may be absorbed into the dry roller excessively, which may cause contamination of the dry roller and cross contamination of the photoreceptor belt, which degrades printing quality.
Third, since the carrier sticking to the photoreceptor belt is not sufficiently evaporated by the dry roller but remains on the photoreceptor belt, the carrier recovery efficiency by the collector is lowered.
Fourth, since the toner image is maintained in a wet state due to the partially dried photoreceptor belt, the toner image is not completely transferred to the sheet of recording paper. Thus, part of the toner image remains on the photoreceptor belt as foreign matter, which considerably degrades the printing quality and contaminates internal components of the printer.
Fifth, due to the incompletely dried photoreceptor belt, the bottom surface of the photoreceptor belt, being in contact with rollers, may be contaminated by the liquid carrier. In this case, a slip occurs between the photoreceptor belt and the driving roller, which disables normal image printing.
Sixth, since the collector for collecting the evaporated gaseous carrier surrounds the dry roller and the heat roller, the overall structure is complex and bulky. Also, since the evaporated carrier contacts the heat roller while in a high temperature state, a fire may be caused in the event of overheating of the heat roller.